There is a technology introduced in the past as a technology for searching for an audio or video content and classifying audio and video contents by providing a keyword to each of the contents. Such a keyword is generally referred to as metadata. In order to assign a keyword to each content, a very large amount of manual work is required as is the case with, for example, a CDDB (CD Database) for providing information such as the names of musical contents recorded on every CD (Compact Disc) serving as a recipient and the names of artists associated with the musical contents. In this case, every time new contents are introduced, manual work is done to register a keyword for each of the contents.
In addition, there has particularly been developed a technology for expressing characteristics of each individual musical content in terms of a numerical value as a technology provided for musical contents and the like, and there is also a technology for inferring metadata such as a keyword from such numerical value.
To put it concretely, there is also an information processing apparatus (such as an apparatus described in Patent Document 1) wherein, in accordance with Quantification Type III, which is a multivariate technique, a discrete quantity such as a keyword given to an individual content is placed in a continuous-quantity space and a canonical correlation analysis is carried out in the continuous-quantity space as well as the space of characteristic quantities in order to obtain a relation associating the continuous-quantity space and the space of characteristic quantities. Then, by making use of the associating relation, a keyword is inferred from a characteristic quantity of a new content.
In addition, there have also been proposed a technique for clustering contents, a technique for clustering keywords (such as a technique described in Patent Document 2), a technique for clustering contents and keywords at the same time (such as a technique described in Non-Patent Document 1) and a technique for recommending a content matching the favorite of a user or matching a context (such as a technique described in Patent Document 3).
The references mentioned above are listed as follows.
[Patent Document 1]    Japanese Patent Laid-open No. Hei 11-96165
[Patent Document 2]    Japanese Patent Laid-open No. 2002-41573
[Patent Document 3]    Japanese Patent Laid-open No. 2001-175676
[Non-Patent Document 1]
Hiroya Takamura and Yuji Matsumoto, “Co-clustering for Text Categorization,” magazine of the Information Processing Society of Japan, Vol. 44, No. 02, an issue of February 2003.